Bleaching cellulosic materials



3,063,783 BLEACHING CELLULOSIC MATERIALS George M. Wagner, Lewiston, N.Y., assignor to Olin Mathieson Chemical Corporation, a corporation of Virginia No Drawing. Filed Mar. 2, 1960, Ser. No. 12,252 4 Claims. (Cl. 8-108) This invention relates to improvements in bleaching using aqueous solutions of chlorites.

In the bleaching of cellulosic textiles, an acid solution of a chlorite gives maximum bleaching with minimum degradation and the production of goods of high whiteness and full strength. A typical bleach bath contains, for example, approximately one gram per liter of sodium chlorite. Sufiicient acid is added to the bath with or without buffering to bring the pH to the desired value, generally to a pH of about 3.5 for cotton goods. Acetic acid is the preferred acid for achieving the pH of 3.5 and formic acid is the preferred acid for solutions of lower pH. Mineral acids, including sulfuric acid and phosphoric acid are also frequently used as acidifying agents. Buffer salts, for example, Na HPO NaH PO or NH HF can be added. In addition, wetting agents which are etfective under acid conditions, for example, the Igepons (salts of acylalkyl taurides) are commonly added. Bleaching baths of these compositions are commonly used at elevated temperatures, for example, 180

F. to 195 F.

Under these conditions of use, the bleaching solutions generate chlorine dioxide rather rapidly, as evidenced by the development of a yellow color in the solution and by the evolution of chlorine dioxide as a gas from the surface of the solution. This generation of chlorine dioxide is objectionable in that the gas lost from the solution represents a loss in bleaching power. It is also objectionable as a health hazard when sufficient chlorine dioxide is evolved to affect workers deleteriously. Chlorine dioxide is an irritating gas and requires removal, for example by means of hoods, from the working space. Furthermore, acid chlorite solutions, particularly when chlorine dioxide is being evolved in the range of pH 2. to pH 4, are corrosive to stainless steels and other metals. These metals become pitted and then corrode at a faster rate than the original highly polished surfaces. In addition, the corrosion products in the solution frequently stain the textile and accelerate further decomposition of the chlorite to chlorine dioxide. Thus, it is necessary, for the most economical and efficient bleaching, to acidity the bleaching bath to form chlorous acid and/ or chlorine dioxide at a rate matching the demand on the solution by the textile being bleached and, at the same time, to avoid producing an excess of chlorine dioxide which would saturate the solution and be evolved as a gas.

Fine adjustment of the pH of the bleaching bath is difficult and, by itself, is inadequate to provide sufiicient chlorine dioxide, as opposed to too much chlorine dioxide. Control of the rate of formation of chlorine dioxide has been attempted by starting the bleach at a moderate temperature, such as 160 F. and a moderate pH of about 4 and adding acid and increasing the temperature during the bleaching period to activate the remaining chlorite more strongly. But such procedures require constant manual attention and it is more desirable, in any event, to add sufficient acid at the beginning for the entire process and to maintain constant temperature.

Considerable control of the corrosion aspect of the excessive chlorine dioxide production problem can be effected by addition to the bleaching bath of nitric acid as the acidifying agent or the addition to the bleaching bath of inorganic nitrates up to a molar ratio of 0.5:1 or more of nitrate to chlorite. For some fabrics, such hanun 3,063,783 Patented Nov. 13, 1962 as Dacron (a polyethylene terephthalate fiber), the use of nitric acid or nitrates has been specified by the manufacturer when chlorite bleaching is employed. Many textile plants, however, regard nitric acid as dangerous to handle. Moreover, control of pH using nitric acid is difficult, since it has no buifering action. Consequently, some mills have preferred to add nitrate salts, e.g., sodium nitrate, to the bath along with the other ingredients and to employ acetic acid as the acidying agent. Acetic acid has a pronounced and useful buffering action, tending to hold the pH value somewhat constant or, at least, minimizing its rise as the bleach bath is used. The addition of sodium nitrate or other nitrate salts to the bath does not interfere with the buffering action. However, there is a limit to the ability of nitrates to retard corrosion of stainless steel in acidified chlorite solutions; to reduce the amounts of corrosion products, particularly iron compounds which cause the decomposition of the chlorite and the production of chlorine dioxide; and to overcome the adverse effects of, for example, iron which may be introduced into the bleach bath from other sources.

One method for lessening the corrosiveness of chlorite baths is to activate the chlorite with formaldehyde, for example, as described in Hampel, US. Patent 2,367,771. In this way the bleaching can take place at a pH of 5 or higher and the corrosion of stainless steel equipment becomes negligible. Although the bath is less acid when formaldehyde is used for activation there is considerable chlorine dioxide evolution because the formaldehyde catalyses its formation. For this reason formaldehyde activation has not met with commercial acceptance in spite of its low cost and effectiveness in bleaching.

It has now been discovered that slightly acidic chlorite solutions are stable and still bleach effectively if formaldehyde and a hydrazide are added thereto. Suitable hydrazides have the formulas: (CONHNH R(CONHNH x R'(CONHNH and R(CONHNH wherein R is selected from the group consisting of hydrogen, saturated hydrocarbon chains and hydroxyl-substituted hydrocarbon chains, R is a saturated hydrocarbon chain interrupted by an oxygen atom and R" is a saturated hydrocarbon chain interrupted by a sulfur atom. Each of the R groups should have less than about 9 carbon atoms. In the formulas, x is a whole number less than 4. Examples of some suitable hydrazides include those of formic, acetic, glycolic, adipic, oxalic, diglycolic, tartaric and citric acids. The use of hydrazides of acids with a higher molecular weight than about that of suberic acid is hampered by water insolubility. However, any organic acid hydrazide which is soluble in water to the extent required can be used. It is surprising that only a very small amount of formaldehyde, in comparison to amounts used in the past, is effective when used in combination with these hydrazides. The hydrazide and the formaldehyde react quickly in aqueous solution to produce compounds whose composition is not definitely known. However, they are water soluble, colorless and stable when used in the dilute solutions of this invention.

According to this invention textiles are bleached with a solution having the following composition:

Parts by Weight Alkali or alkaline earth metal chlorite 0.002-2.0 Formaldehyde or paraformaldehyde 0.002-0.05 Hydrazide 2 to 10 times CH O Water formed in solution. They can hold the pH in the preferred range of 5.5 to 7.0 and have a beneficial effect on the degree of bleaching. Other substances can also be used as buffers as long as they are non-reactive with any of the bleach bath components. The use of more hydrazide than about times the formaldehyde weight is uneconomical and has no further effect. A ratio of less than 2 parts of hydrazide to formaldehyde can, under certain conditions, cause precipitation of polyrnethylol hydrazide polymers. Using such a bath the textile can be bleached in the bath in about one or two hours at 80 C. to 100 C. Alternatively, the textile can be passed through the bath at room temperature and the excess liquid expressed from the cloth by passing it between rollers at suitable pressure. The cloth is then heated at 80 C. to 100 C. for one or two hours to effect the bleaching. The heating should be done in a steam box or other suitable apparatus which provides a hot, humid atmosphere substantially saturated with water vapor to prevent the cloth from losing moisture during this bleaching period. A suitable solution content on the cloth to be heated is 80% to 150% by weight based on the weight of the cloth.

The method of this invention can be used to bleach textiles which are blends of different fibers, for example cotton-rayon or cotton-Dacron blends; especially those having 50% or more of cellulosic material. The term cellulosic textile as used in this specification and claims is meant to include cotton, linen, regenerated cellulose (rayon) and textile blends containing non-cellulosic fibers, but having about 50% or more of cellulosic fibers. The following examples illustrate several of the various embodiments of this invention:

Example I Several portions of cotton broadcloth were passed through an aqueous solution containing 0.8% by weight of sodium chlorite, 0.5% of diglycolic hydrazide, 0.02% of formaldehyde, enough acetic acid to bring the pH to about 5.5 and 0.23% of sodium nitrate as corrosion inhibitor. The cloths were squeezed to contain a weight of solution equal to their own and then maintained in an atmosphere saturated with water vapor at 90 to 100 C. for one hour. They were then removed, rinsed and dried and had an average brightness of 87.7 units, compared to an original value of 63 units.

Example 11 An aqueous bleach bath was prepared containing the following components in percentages by Weight based on the entire bath:

Example Ill Two bleach baths were made up having the following compositions in parts by weight:

Component A B Sodium chlorite 0.8 0.8 Glycolic hydrazide 0. 4 Formaldehyde 0. 2 Oyzmuric acid 0.1 0. 1 Water 09 99 Example IV Two solutions were made up having the following composition in parts by weight:

Component A B Sodium chlorite. 0.8 0.8 Acetic hydrazide 0. 5 Formaldehyde 0. 05 0. 05 Water 99 99 Acetic acid was added to both solutions to bring the pH to 6.0. The solution containing no acetic hydrazide promptly began liberating chlorine dioxide to the atmosphere while the solution containing the hydrazide liberated no discernable chlorine dioxide for 16 hours.

Example V A bleach bath Was made up having the following composition.

Component: Parts by weight Potassium chlorite 1.65 Propionic hydrazide 0.019 lFormaldehyde 0.0027 Water 98 Cyanuric acid was added to the above bath until the pH was 6.8. The bath was heated to 97 C. and a section of huckaback toweling having an original brightness of 63 was immersed therein for 1 hour and 35 minutes. The cloth was removed from the bath, rinsed and dried. It then showed a brightness of 82.

Example VI A section of cotton broadcloth was padded with a solution prepared by mixing the following substances.

Component: Grams Water 18,000 Diglycolic hydrazide 9 Paraformaldehyde 2 Sodium nitrate 43 Cyanuric acid 27 Sodium chlorite 150 The cloth picked up a weight of solution equal to its own dry weight and was placed in na atmosphere saturated with water vapor at 100 C. for 1 hour. After this heating period, the cloth had a brightness of 84.5 in comparison with an initial brightness of 59.

What is claimed is:

1. The method of bleaching cellulosic textiles which comprises heating the textile at a temperature of about C. to C. in contact with an aqueous solution, acidified to a pH of 5 to 7, prepared by admixing water, a chlorite, selected from the group consisting of alkali metal chlorite and alkaline earth metal chlorites, formaldehyde and a hydrazide having a formula selected from the group consisting of: (C0NHNH moomnrup R(CONHNH and R"(CONHNH wherein R is selected from the group consisting of hydrogen, saturated hydrocarbon chains and hydroxyl-substituted hydrocarbon chains, R is a saturated hydrocarbon chain interrupted by oxygen, R is a saturated hydrocarbon chain 5 interrupted by sulfur, each of said R, R' and R having less than 9 carbon atoms and x is an integer less than 4; said ingredients being admixed in the proportions of 100 parts of water, 0.002 to 2.0 parts of chlorite, 0.002 to 0.05 part of formaldehyde and 2 to 10 parts of hydrazide per part of formaldehyde added to the composition.

2. The method of claim 1 wherein the bleaching is effected by keeping the cloth immersed in the body of prepared solution and maintaining the solution temperature at 80 C. to 100 C.

3. The method of claim 1 wherein the bleaching is effected separately from the impregnation step by heating the wet cloth at 80 C. to 100 C. in an atmosphere substantially saturated with water vapor to effect bleaching.

4. The method of claim 1 wherein the hydrazide is diglycolic hydrazide and the chlorite is sodium chlorite.

References Cited in the file of this patent UNITED STATES PATENTS Hampel Jan. 23, 1945 Hampel Oct. 21, 1947 Hampel Nov. 11, 1947 Hampel Nov. 11, 1947 Hawkinson July 7, 1959 Holbrook et a1 Sept. 15, 1959 Holbrook et al. Sept. 15, 1959 Holbrook et al Sept. 15, 1959 Waibel Aug. 2, 1960 FOREIGN PATENTS Great Britain Mar. 31, 1954 

1. THE PROCESS OF BLEACHING CELLULOSIC TEXILES WHICH COMPRISES HEATING THE TEXILE AT A TEMPERATURE OF ABOUT 80*C. TO 100*C.IN CONTACT WITH AN AQUEOUSS SOLUSTION, ACIDIFIED TO A PH OF 5 TO 7, PREPARED BY ADMIXING WATER, A CHLORITE, SELECTED FROM THE GROUP CONSITING OF ALKALI METAL CHLORIDE AND ALKALINE EARTH METAL CHLORITES, FORMALDEHYDE AND A HYDRAZIED HAVING A FORMULA SELECTED FROM THE GROUP CONSITING OF;(CONHNH2)2, 